The cells to which the catalyst electrode of this invention are applicable include fuel cells using alkaline electrolytes, air zinc cells for stationary or installation use, etc. but is particularly useful for the air-zinc button cell.
The catalyst materials heretofore explored from very early times to the present day are various metals and metal oxides, activated carbon, carbon, etc. Thus, noble metals such as metals of the platinum group and silver as deposited on activated carbon or carbon black, mixtures of metal oxides with carbon, and mixtures of metal phthalocyanine complexes with carbon, whether heat-treated or not, may be mentioned by way of example.
Generally, noble metal elements represented by platinum and palladium have relatively high catalyst activity but when the difficulty of regeneration for reuse is taken into consideration, as it is important in the case of primary cells such as air-zinc button cells, noble metal catalysts have the disadvantage that they cannot be provided at low cost.
For the above reason, it has been attempted over years to explore the use of manganese oxide as an inexpensive catalyst for air cell use. For example, U.S. Pat. Nos. 3,948,684, 4,121,018 and 4,269,691 teach such catalysts. According to these patents, various types of chemical manganese are subjected to chemical or heat treatment so as to precipitate MnO.sub.2, Mn.sub.2 O.sub.3 or/and Mn.sub.3 O.sub.4 on carbon or mix .gamma.MnO.sub.2 with carbon and alkali to constitute a catalyst.
As pointed out in the aforementioned United States Patents, manganese oxides have catalyst activity and some of them have satisfactory discharge characteristics at a current not exceeding several mA/cm.sup.2 but these oxides are not necessarily fully satisfactory in high-rate discharge at a current of more than 10 mA/cm.sup.2 and in discharge characteristics after storage. Under the circumstances there has been demanded a manganese oxide having improved catalyst activity and storage stability.